Self-convergent deflection yoke for a color tv cathode ray tube and system using the same



April 14, 1959 5, RElCHEs 2,882,431

' SELF-CONVERGENT DEFLECTION YOKE F OR A COLOR TV CATHODELRAY TUBE AND SYSTEM USING THE SAME 3 Sheets-Sheet 1 Filed Nov. 13 1956 Aprll 14, 1959 s. L. REICHES 2,882,431

SELF-CONVERGENT DEFLECTION YOKE FOR A COLOR TV CATHODE RAY TUBE AND SYSTEM USING THE SAME File-d Nov. 13, 1956 3 Sheets-Sheet 2 INVENTOR.

L. R SELF-CONVERGENT DEFLECTION YOKE FOR A COLOR TV CATHODE RAY TUBE AND SYSTEM USING THE SAME April 14, 1959 s EICHESA 2,882,431

Filed Nov. 13, 1956 3 Sheets-Sheet 3 INVENT OR.

after- 29v SELF-CONVERGENT DEFLECTION YOKE FDR A COLOR TV CATHODE RAY TUBE AND SYSTEM USING THE SAME Sol L. Reiches, Shaker Heights, Ohio, assignor to Park Products Company, Cleveland, Ohio, a corporation of Ohio Application November 13, 1956, Serial No. 621,582

Claims. (Cl. 313-76) My invention relates to an improved self-convergent deflection yoke for a multi-gun color TV cathode ray tube and system using the same, whereby convergence of the beams from the guns is improved over the entire sweep cycle by an auxiliary coil in the yoke.

In one type of color television cathode ray tube an electron beam constituting a stream of electrons is emitted from each of a plurality of electron guns, one for each basic color, toward the viewing screen of the tube. The viewing screen has a plurality of sets of phosphor dots, each set comprising a dot for each basic color, such as red, blue, and green. Each color dot emits light of that color when struck by a beam from the corresponding electron gun. The dots of each set are clustered in sets on the viewing screen so that each elemental area on the viewing screen has a set of dots capable of producing light which is colored depending on which dot or dots are struck by the electron beams. A shadow mask, which is a thin arcuate plate of the same conformation as the viewing screen and has a plurality of small openings, one for each set of dots, is located between the electron guns and the viewing screen, close to the latter surface.

Between the electron gun and the viewing screen of the tube a magnetic deflection yoke encircles the neck of the tube. The electron guns are positioned within the neck of the tube and emit electron beams directed to the viewing screen which pass through the zone of influence of the yoke to be deflected thereby. These beams are in spaced relation to each other and are oriented in nearly parallel relation to the axis of the tube.

It is evident that, for color purity, the electron beams from the respective guns must at any one time be oriented to strike a single set of dots, with the electrons from each gun striking its corresponding dot of the set. Proper convergence is achieved only when the respective beams.

converge at or closely behind the shadow mask. The openings in the shadow mask are positioned so that, with proper convergence at the shadow mask, each beam strikes its respective dot. A time-constant magnetic field is provided to bend the electron streams toward each other to provide this convergence in the absence of a sweep current flow through the yoke. The time-varying magnetic sweep field produced by the sweep windings acts on the electron beams to sweep them in unison across the viewing screen in a succession of lines to reproduce the television irnage. The beams from the respective electron guns should converge on the shadow mask at all times during the sweep cycle.

It has been found that in color TV tubes with conventionaldeflection yokes convergence is not achieved at all points on the viewing screen. If the time-constant magnetic field is adjusted properly to converge the electron beams at the center of the shadow mask, a loss of convergence will occur as the edges of the screen are approached. In present equipment the paths of the electron beams from the guns tend to cross inside the tube and upstream from the shadow mask, as the beams sweep from the center of the shadow mask to define a locus of convergence having smaller radius of curvature than the shadow mask. Consequently, as the electron beams are swept towards the margins of the viewing screen, the convergence is destroyed and color purity lost.

In the present invention an improved yoke is provided which increases the degree of convergence of the electron beams over all areas of the screen. In brief, the yoke of the present invention has a pair of opposed sweep windings which are carried on the yoke to straddle the neck of the tube. Each of these windings defines a window. A pair of opposed short circuited auxiliary coils are located in the windows of the respective windings. When a time-varying voltage is applied to the sweep windings, a time-varying sweep magnetic field is established normal to the longitudinal axis of the neck of the tube and through the axis of the coils. Simultaneously a current is induced in the short circuited auxiliary coils. This current is of direction and magnitude to oppose the flux produced by the sweep windings. Since the coils are small in relation to the sweep windings, and are positioned within the confines of the windings, the sweep magnetic field is altered only in the central portion adjacent the axis defined by the sweep windings. In this area the magnitude of the time-varying magnetic field is substantially less than it would be without the auxiliary coils, while in the area on either side of this central portion the magnetic field produced by the windings is determined to a greater extent by the current flow in the sweep windings.

When the current in the sweep windings is large, the magnitude of the field produced by this current will be large and the electron beams from all the guns will be deflected to one side of the viewing screen adjacent one margin. A beam of electrons emitting from a gun spaced from the longitudinal axis of the neck of the tube in the direction toward that margin of the viewing screen will be relatively unaffected by the action of the auxiliary coils since the beam will not pass close to the axis defined by the sweep coils. However, a stream of electrons emitting from a gun spaced from the axis of the sweep coils in the direction away from the direction of deflection will pass close to the axis of the sweep coils and hence through a space of lesser field intensity. This beam will, therefore, have a total angle of deflection which is smaller than it would have without the action of the auxiliary coils. By reducing the angle of deflection of this latter beam, without appreciably affecting the angle of the former beam, the paths of the streams will tend to remain convergent at the shadow mask.

It is therefore a general object of the present invention to provide an improved self-convergent deflection yoke fora TV cathode ray tube having a plurality of electron guns which will deflect the beams across the viewing screen of the tube in unison without loss of convergence.

It is another object of the present invention to provide a device for improving convergence of a plurality of electron beams in a TV color cathode ray tube which can be located in a small, normally unused, space.

It is still another object to provide a simple multiple ray beam converging device requiring no independent source of energy nor magnets.

It is a further object of the present invention to provide a multi-gun cathode ray tube deflection yoke having auxiliary coils which alter a portion only of the sweep magnetic field.

It is another object of the present invention to provide a multi-gun color TV cathode ray tube and yoke therefor in which the beams from the guns will properly converge during the entire sweep cycle.

A further and additional object of the present invention is to provide an improved self-convergent yoke assembly for a multi-gun cathode ray tube in which auxiliary coils located within the confines of the main sweep windings serve to modify selectively a portion of the sweep field in such fashion as to prevent the loss of ray beam convergence otherwise experienced.

It is an additional object of the present invention to provide a self-convergent deflection yoke for a. multi-gun TV cathode ray tube which is of simple construction, requires little space, is positive in its action, and eflectively improves convergence.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will be best understood by reference to the following description taken in conjunction with the accompanying drawings in which:

Figure 1 is an elevational view of a color TV multi-gun cathode ray tube, with parts broken away, and the selfconvergent yoke installed on the neck;

.Figure 2 is a top plan view of the TV tube of Figure l, with the self-convergent yoke shown in schematic form, showing the paths of the electron beams from the electron guns when focused on the center of the shadow mask and when focused on one side of the shadow mask.

Figure 3 is a view through section 3-3 of Figure 1;

Figure 4 is a view through section 4-4 of Figure 1;

Figure 5 is a view through section 5-5 of Figure 3;

Figure 6 is a top plan view of a multi-gun cathode ray tube,,with parts broken away, showing the path followed by the electron beams from the electron guns when a conventional yoke is used; and

Figure 7 is a schematic view through the neck of a TV cathode ray tube looking toward the electron guns showing the position of the yoke winding and auxiliary coils, without supporting structure, and the magnetic field produced thereby.

A TV color television tube with the yoke of the present invention installed thereon is shown in Figure 1. The tube, shown generally at 10, is a glass bulb having a flared portion 12, a viewing screen 14 and a neck portion 16. The neck portion has a longitudinal axis AA. Within the neck are three electron guns 221', 22b, and 22g which are circumferentially spaced around the longitudi nal axis of the neck and at equal radial and angular spacings as shown in Figure 7. Each of the guns, when energized, emits a beam constituting a stream of electrons directed toward the viewing screen 14 of the tube along an axis nearly parallel to axis AA. The viewing screen 14 has a phosphor coating 18 on its inner surface. The phosphor coating is made up of a plurality of sets of dots. Each set of dots has one dot corresponding to each electron gun. When each such dot is struck by electrons it produces light of a particular color, such as red, blue, or green. A shadow mask 20 having an arcuate surface 20a is interposed between the phosphor coated screen 14 and the electron guns and has an array of openings (not shown), one for each set of dots. The dots of each set are so located behind these openings as to receive the corresponding electron beam and not the other electron beams, thus providing color sensitivity.

As shown in Figure l, the yoke encircles the neck 16 of the tube with the downstream end of the yoke 24a, in relation to beam travel, adjacent the flared portion 12 of the tube. Permanent magnet means 25, which produces a time-constant magnetic field which may be adjusted to bend the ray beams to converge on the center of the shadow mask 20 in the absence of sweep, encircles the neck of the tube adjacent the upstream end 241), in relation-to beam travel, of the yoke 24. Alternately, the electron guns may be oriented to emit electron beams whichrtravel at a slight angle to the axis of the neck of the tube and converge, without the necessity of permanent magnet means, at the center of the shadow mask i he absence of sweep.

The yoke 24 is shown in Figures 3, 4, and 5. The yoke has an outer casing shown generally at 26. The casing has a cylindrical center portion 26a and an annular flange 26b extending radially outward at the rear, or upstream, edge of the cylindrical portion. The flange 2612 has a rearwardly extending rim 260 at its outer edge. At

the forward, or downstream edge of the center portion 7 of the casing there is a flared portion 26d extending outwardly and forwardly. An annular flange 26e is connected to and extends radially outward from the outer edge of the flared portion 260?. A non-metallic collar 27 snugly encircles the center portion 26a.

The yoke 24 has a rubber sheath, shown generally at 28, which is received inside the casing 26. As shown in Figure 5, the sheath has a central cylindrical portion 28a. The inner diameter of the cylindrical portion is sutficiently large to receive the neck 16 of the tube. The outer surface of the cylindrical portion is spaced from the inner surface of the cylindrical portion 26a of the casing. The sheath 28 has a rear annular flange 2817 which snugly fits inside the rim 260 of the casing. The flange 28b of the sheath is spaced from the flange 26b of the casing. At the forward end of the cylindrical center portion a flared portion 28c extends outwardly and forwardly and is spaced from the flared portion 26d of the casing. The inner surface of the central portion 28a of the sheath has a pair of ribs 28d protruding therefrom positioned opposite each other and centrally on the sides. The ribs extend over a portion of the forward flared portion 28c of the sheath.

The yoke has a pair of opposed horizontal sweep windings 30 and having an axis B-B at right angles to the axis AA of the neck and disposed to produce a vertically oriented magnetic field. The windings 30 straddle the neck 16 of the tube with one of the windings carried on the upper half of sheath 28 above the ribs 281; and the other winding carried on the lowerhalf of the sheath below the ribs 28b. Each winding is carried on the forward face of the flared portion 28c, the inner surface of the central portion 28a, and the rear face of flange 28b. The portions of the two windings carried on the inner surface of the central portion 28b of the sheath define a generally cylindrical face. Each winding has a window 30a within its confines which, as shown in Figure 5, extends substantially in all directions about the axis of the windings.

The yoke also has a pair of opposed vertical sweep windings 32 which are spaced circumferentially from the horizontal windings 30 to produce a horizontal magnetic field. The vertical sweep windings 32 are sandwiched between the sheath 28 and the casing 26. A per-1 tion of the windings 32 is interposed between the rear flange 28b of the sheath and the rear flange 26b of the. casing, a portion is interposed between the central portion 28a of the sheath and the central portion 26a of the casing, and a portion is interposed between the forward flared portion 28c of the sheath and the forward flared portion 26d of the casing.

In accordance with the present invention the yoke 24 also has a pair of opposed auxiliary coils 34. Each of the coils 34 is glued flat to the inner surface of the sheath 28 to lie in the window 30a within the confines of the horizontal sweep windings 30 so that at least a portion of the coil is in the same general cylindrical surface as the windings. The auxiliary coils are preferably located in the downstream portion of the windows 3011, in rela tion to beam travel. The coils are preferably of triangular configuration having an apex 34a at the upstream end of the coil and a base 34b at the downstream end of the coil. The apex 34a lies on the inner surface of. the central cylindrical portion 28a of the sheath and the base 34b lies on the forward surface of the forward flared portion 280 of the sheath.

In operation a beam of electrons is emitted from each' gun 22 Z23. and-22b, directed toward the viewingscreen as shown in Figure 2. Initially the paths of these beams. of electrons. are nearly parallel to the axis of the neck of the tube. When no current is flowing in the windings 30 and the auxiliary coils 34 no magnetic field is produced and the streams of electrons strike the center of shadow mask 20. A device 25 having permanent magnets is provided to bend the beams together to converge on the shadow mask 20. If proper convergence at the shadow mask is achieved the beam 36r from the gun 221' will strike the dot in the set which gives off red light, the beam 3611 from the gun 22b will strike the dot in. the same set which gives off blue light, and the beam 36g from the gun 22g will strike the dot. of that set which gives off green light. When, during the sweeping opera.- tion, current is passed through the horizontal windings '30 the three electron beams 361', 36b and 36g, are de- 'fiected in unison to one side of the viewing screen. When no auxiliary coils 34 are used there is a tendency for the beams from the guns to cross inside the shadow mask, rather than converge on the shadow mask, as shown in Figure 6, even though proper convergence is obtained at the center. of the shadow mask.

With the yoke of the present invention proper convergence will be achieved even when the electron beams are deflected during the sweeping operation. This is because of the action of the auxiliary coils 34. As shown in Figure 7 a time varying magnetic field is produced when a time varying current flows in the horizontal sweep winding 30. This field is substantially uniform in the area through which the beams from the electron guns pass. The sweep windings are normally energized with asa'w tooth sweep current to sweep the ray beams repetitively across the viewing screen and shadow mask in a television scanning raster. The magnetic field produced by the sweep current induces in the auxiliary short circuited windings 34 a current which tends to oppose the fiux producedby the sweep windings 30. However, since the auxiliary coils 34 are relatively small in comparison with the sweep windings 30 and are positioned within the confines of those windings and to straddle the axis of the tube, the influence of the current in the coils 34 will not be over the entire magnetic field produced. by the windings 30. Instead, the effect of the current in the coils 34 will be limited to a portion of the magnetic field passing through the center of the neck of the tube. For this reason the change in the magnetic field of the sweep windings effected by the auxiliary coils 34 will not influence the path of travel of all of the streams of electrons in the same manner. For example, referring to Figure 2, it will be noted that the gun 22r is spaced from the longitudinal axis of the neck of the tube in the direction of deflection as shown in that figure. On the other hand, the gun 22g is spaced from the horizontal axis of the neck of the tube in the direction away from the direction of deflection. Thus, a beam Stir from the gun 22) will not cross the central portion of the neck of the tube as it flows to the deflected position on the viewing screen. On the other hand, the beam 36g from the gun 22g must pass through the central portion of the neck of the tube in order to reach the deflected position. Thus the beam 36r will pass through only that port on of the magnetic field which is relatively unafifected by the action of the auxiliary coils 34. On the other hand, the beam 22g must pass through the area which 1s mfluenced by the action of the coils 34. Since, when the coils are short-circuited, they reduce the strength of the magnetic field in the area of their influence, the beam 22g will be deflected less than it would be if there were no auxiliary coils. Since the beam 361' is relatively unaffected by the auxiliary coils 34 and the beam 36g w1ll deflect less under their action the beams will not cross inside the tube but instead will converge on the shadow mask 20.

Thus by the improved yoke of the present invention proper convergence of thebeams from a plurality of electron guns of a colored TV tube can be maintained, not only at the center portion of the shadow mask, but also across its entire area. This is made possible by the action of a pair of auxiliary coils which affect the magnetic field produced by the sweep windings in the region near the tube axis. B'y positioning the auxiliary coils within the sweep windings it is possible to alter thepath of the beams of electrons passing near the tube axis in relation to the other electron beams thereby selectively shifting the positions of the electron streams in such fashion as to maintain convergence at the shadow mask.

it will be understood that the exact number of turns in the auxiliary coils 34 and their distribution is a matter of engineeringdesign and that these may be chosen as required to accommodate specific tube constructions. For example, a single turn for each winding 34formed from a copper stamping-may suffice in some instances and has the advantage of low cost and ease of mounting. On the other hand, with unusual conditions of required correction it may be necessary to use a considerable number ofturns having a specific configuration within the main sweep windings. It will, of course, be understood that all these modifications and alternative constructions fall within the true spirit and scope of the present invention.

While I have shown and described a specific embodiment of the present invention it will be understood that numerous modifications and alternative construction may be made without departing from its true spirit and scope. In the above description I have referred to the phosphor coating on the screen. as being made up of a plurality of sets of dots. It will of course be understood that I have described this particular construction of the screen merely for purposes of illustration and that the present invention can be used in any TV cathode ray tube having guns spaced from a longitudinal axis where convergence of the beams from the guns is desired. Also, the auxiliary coils have been shown and described as being positioned within the confines of they horizontal sweep windings.

Obviously, if required, the. auxiliary coils could also, or alternately, be used in connection with the vertical sweep windings. I therefore intend by the appended "claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

i l. A self-convergent magnetic yoke assembly for a multrple ray beam cathode ray tube having a neck with an axis, a plurality of electron guns located in the neck in spaced relation to the axis, and an arcuate surface upon which, the ray beams should converge to reproduce a television image, the electron beams from the guns. con.- verging. on the surface at said axis in the absence of sweep, the yoke assembly comprising: a pair of windings straddlmg the neck of said tube, the windings being adapted to produce a magnetic field encompassing said neck and transverse to said axis to cause ray beam sweep; and a pair of auxiliary short circ yited coils located within the confines of the windings, respectively, and encompassing only a centered portion of the neck of the tube to reduce the magnitude. of the magnetic field variations in the area of the axis of the tube and compensate for the loss of ray beam convergence otherwise associated with sweep of thev ray beams away from the axis of the tube.

2. A self-convergent magnetic yoke assembly for a sweep, the yoke assembly comprising: a pair of windings straddling the neck of the tube and having an axis at'right angles to the axisof the neck, said windings. having a gene r h V 2,852,431

erally cylindrical inner face defining an opening to receive the neck of the tube and having a portion at the downstream end as to ray beam travel extending outwardly from the axis of the neck of the tube, each winding defining a window, a portion of which is within the outwardly extending portion of the winding, whereby sweep current flow through the windings produces a magnetic field of substantially uniform intensity in the regions traversed by the electron beams; and a pair of auxiliary I coils located within the windows defined by the windings and positioned in the windows in the downstream end thereof as to ray beam travel, the coils having a triangular conformation with the apex located at the upstream end of the coils as to ray beam travel, and the base located at the downstream end of the coils within the portion of the windings extendingoutwardly from the axis, whereby the coils modify the magnetic field in the region of the neck axis and overcome the effect of the windings in destroying convergence as the ray beams are swept.

3. A self-convergent magnetic yoke assembly for a cathode ray tube of the type having a neck with an axis, a plurality of electron guns located in the neck in spaced relation to the axis, means defining a surface upon which the ray beams should converge to reproduce a television image in color, the electron beams from the guns converging on the surface at said axis in the absence of sweep, the yoke assembly comprising: a pair of windings straddling the neck of the tube and having an axis at right angles to the axis of the neck, said windings having a generally cylindrical inner face defining an opening to receive the neck of the tube and defining windows of substantial extent in all directions about the axis of the windings, whereby sweep current flow through the windings produces a magnetic field of substantially uniform intensity in the region traversed by the electron beams; and, a pair of auxiliary coils located within the windows defined by the windings with at least a portion of each coil in substantially the same cylindrical surface as said windings, the coils being located on the half of each win dow in the downstream position as to ray beam travel and having substantially triangular conformation with the apex located at the upstream position as to ray beam travel, whereby the coils modify the magnetic field in the region of the neck axis and overcome the elfect of the windings in destroying convergence as the ray beams are swept.

4. A self-convergent magnetic yoke assembly for a multiple ray beam cathode ray tube having an arcuate surface upon which the ray beams should converge, a neck with an axis, a plurality of electron guns operable to produce ray beams, the guns being spaced from said axis, and having means to orient the ray beamsto convergent relation at a point on said surface in the absence of sweep action, the yoke comprising: a winding adjacent the neck of said tube adapted to produce a magnetic field through said neck and transverse to the axis of the neck to cause ray beam sweep; and a short circuited auxiliary coil 1ocated within the confines of the winding adapted to reduce said magnetic field through only a portion of the neck in the area of the axis of the neck of the tube and compensate for the loss of ray beam convergence otherwise associated with the sweep of the ray beams away from the axis of the tube.

5. In combination, a cathode ray tube having a neck with an axis, a plurality of electron guns located in the neck and operable to produce ray beams oriented parallel to the axis, and means defining an arcuate surface upon which the ray beams should converge to reproduce a television image in color; means operable to bend the ray beams to converge on said surface in the absence of sweep; and, a magnetic sweep unit operable to sweep the ray beams in unison over said surface, said unit including a winding adapted to produce a magnetic field extend ing over substantially the entire portion of the tube neck occupied by the ray beams and oriented at right angles to said axis, whereby a saw tooth sweep current sweeps the ray beams in unison across said surface, said unit further having an auxiliary coil forming a flux linkage path extending over a fragmentary portion of the field of said winding in the area of the axis of the tube to alter the space distribution of the flux of said winding and thereby vary the eifective flux density experienced by the ray beams as they are deflected towards the axis of the tube and overcome the effect of the winding in destroying convergence as the ray beams are swept.

6. A self-convergent magnetic yoke assembly for a multiple ray beam cathode ray tube having a neck with an axis, a plurality of electron guns located in the neck in spaced relation to the axis, and an arcuate surface upon which the ray beams should converge to reproduce a television image, the electron beams from the guns converging on the surface at said axis in the absence of sweep, the yoke assembly comprising: a pair of windings straddling the neck of said tube, the windings being adapted to produce a magnetic field encompassing said neck and transverse to said axis to cause ray beam sweep, each winding defining a window; and a pair of auxiliary short circuited coils in the windows of the windings, respectively, at the downstream end thereof as to ray beam travel, and encompassing only a centered portion of the neck of the tube to modify the magnetic field in the region of the neck axis and overcome the effect of the windings in destroying convergence as the ray beams are swept.

7. A self-convergent magnetic yoke assembly for a multiple ray beam cathode ray tube having a neck with an axis, a plurality of electron guns located in the neck in spaced relation to the axis, and an arcuate surface upon which the ray beams should converge to reproduce a television image, the electron beams from the guns converging on the surface at said axis in the absence of sweep, the yoke assembly comprising: a pair of windings straddling the neck of said tube, each winding having a flared portion extending outwardly from the axis of the tube and each winding having a window a portion of which is within the flared portion of the winding; and a pair of auxiliary short circuited coils in the windows of the windings and encompassing only a centered portion of the neck of the tube, each of the coils having a flared portion extending outwardly from the axis of the tube within the flared portion of the winding, whereby the magnetic field in the region of the neck axis is modified to overcome the effect of the windings in destroying con- 1 vergence as the ray beams are swept.

8. In combination, a cathode ray tube having a neck with an axis, a plurality of electron guns located in the neck and operable to produce ray beams oriented parallel to the axis, and means defining an arcuate surface upon which the ray beams should converge to reproduce a television image in color; means operable to bend the ray beams to converge on said surface in the absence of sweep; a magnetic sweep unit operable to sweep the ray beams in unison over said surface, said unit including a pair of windings straddling the neck of the tube and having an axis at right angles to the axis of the neck, said windings defining windows of substantial extent in all directions about the axis of the windings, whereby sweep current flow through the windings produces a magnetic field of substantially uniform intensity in the region traversed by the electron beams; and, a pair of auxiliary coils located within the windows defined by the windings, the coils being located in the downstream part of the windows as to ray beam travel, whereby the coils modify the magnetic field in the region of the neck axis and overcome the effect of the windings in destroying convergence as the ray beams are swept.

9. In combination, a cathode ray tube having a neck with an axis, a plurality of electron guns located in the upon which the ray beams should converge to reproduce a television image in color; means operable to bend the ray beams to converge on said surface in the absence of sweep; a magnetic sweep unit operable to sweep the ray beams in unison over said surface, said unit including a pair of windings straddling the neck of the tube and having an axis at right angles to the axis of the neck, said windings having a generally cylindrical inner face defining an opening to receive the neck of the tube and defining windows of substantial extent in all directions about the axis of the windings, whereby sweep current flow through the windings produces a magnetic field of substantially uniform intensity in the region traversed by the electron beams; and, a pair of auxiliary coils located within the windows defined by the windings with at least a portion of each coil in substantially the same cylindrical surface as said windings, the coils being located on the half of each window in the downstream position as to ray beam travel and having substantially triangular conformation with the apex located at the upstream position as to ray beam travel, whereby the coils modify the magnetic field in the region of the neck axis and overcome the effect of the windings in destroying convergence as the ray beams are swept.

10. A self-convergent magnetic yoke assembly for a cathode ray tube of the type having a neck with an axis, a plurality of electron guns located in the neck in spaced relation to the axis, means defining a surface upon which the ray beams should converge to reproduce a television image in color, the electron beams from the guns converging on the surface at said axis in the absence of sweep, the yoke assembly comprising: a pair of windings straddling the neck of the tube and having an axis at right angles to the axis of the neck, said windings having a generally cylindrical inner face defining an opening to receive the neck of the tube and defining windows of substantial extent in all directions about the axis of the windings, whereby sweep current flow through the windings produces a magnetic field of substantially uniform intensity in the region traversed by the electron beams; and, a pair of auxiliary coils located Within the windows defined by the windings with at least a portion of each coil in substantially the same cylindrical surface as said windings, whereby the coils modify the magnetic field in the region of the neck axis and overcome the efiect of the windings in destroying convergence as the ray beams are swept. 

